I came kinda close one night when I was out partying at Liquid Joes. I was already going to be out all night cause I was sleeping in my Xterra in front of a friends house and my wife knew that so I didn't need to come home that night. I was out smoking and an extremely attractive female came over and struck up a convo with me and we were vibing pretty good and she asked where I was going after the club/bar and I said to a friends house and she was like "well I will be your friend tonight if you want to stay at my house" and it was tempting. Plus being drunk made me consider it when I never would sober.
Im very glad I turned her down. The guilt would have destroyed me and I would have came clean, probably got a divorce and never had my daughter.
Thats the only time I have ever came close.
Never really cheated on a girlfriend either though there was a gray area when I broke up with a girlfriend, slept with a co worker at a cabin, and then got back together with my girlfriend all in about a 5 day span. That was pretty shady of me.